An anesthetic vaporizer is an apparatus that can be used to effectively vaporize a liquid anesthetic agent, and can precisely input the liquid anesthetic agent at a certain concentration into an anesthesia breathing circuit, which is able to eliminate the influences of changes in temperature and pressure and the like on the concentration output thereof.
As illustrated in FIG. 1, the anesthetic vaporizer typically comprises a fresh gas inlet 1′, a pressure compensation unit 2′, a fresh gas control valve 3′, a wick unit 4′, a bypass circuit 5′, a temperature compensation unit 6′, a concentration control unit 7′, a mixed gas outlet 8′, a filling unit 9′, and a vaporizing chamber 10′. The fresh gas inlet 1′, the bypass circuit 5′, the temperature compensation unit 6′, the concentration control unit 7′ and the mixed gas outlet 8′ are sequentially connected with one another; while the fresh gas inlet 1′, the pressure compensation unit 2′, the fresh gas control valve 3′, the wick unit 4′, the concentration control unit 7′ and the mixed gas outlet 8′ are sequentially connected with one another. The vaporizing chamber 10′ has a reservoir for storing anesthetic agent. A part of the wick unit 4′ is immersed into the anesthetic agent. The pressure compensation unit 2′ is positioned outside the reservoir of the vaporizing chamber 10′. The reservoir of the vaporizing chamber 10′ is through a passage connected to the filling unit 9′ for injecting the anesthetic agent into the reservoir.
Fresh gas flows into the vaporizer through the fresh gas inlet 1′. A part of the gas flows into the wick unit 4′ through the fresh gas control valve 3′ after passing through the pressure compensation unit 2′. A part of the wick unit 4′ is immersed into the anesthetic agent so that the wick unit 4′ is filled with the saturated vapor of anesthetic gas. When the fresh gas flows through the wick unit 4′, the fresh gas will be mixed with parts of the anesthetic vapor. The fresh gas carrying the anesthetic vapor flows into the concentration control unit 7′ after passing through the wick unit 4′. The other part of the fresh gas flows into the bypass circuit 5′ of the vaporizer, then flows into the concentration control unit 7′ after passing through the temperature compensation unit 6′, and meets the fresh gas carrying the anesthetic vapor in the concentration control unit 7′. By the controlling of the concentration control unit 7′, the two streams of gases are mixed at a certain ratio and outputted out of the vaporizer from the mixed gas outlet 8′.
When the vaporizer is used continuously, the temperature of the vaporizer drops since the anesthetic agent has to absorb heat to vaporize, which in turn reduces the evaporation speed of the anesthetic agent since the evaporation speed of the liquid decreases as the temperature drops. Thus, the concentration of the anesthetic vapor outputted from the vaporizer is reduced accordingly. In order to prevent the concentration of the vaporizer from changing due to temperature dropping, in the vaporizer being subjected to temperature change, the temperature compensation unit 6′ will change the vent aperture of its valve opening to increase or decrease the gas flow of the bypass circuit 5′, so that the concentration output of the vaporizer does not change according to temperature change. The temperature compensation unit 6′ may be implemented as a valve body which may control the gas flow of the bypass circuit 5′, the operation principle of which is to take advantage of the difference between the expansion coefficients of different metals to change the size of the temperature compensation valve opening so as to change the vent aperture for the gas.
The pressure compensation unit 21 has two main functions as follows: (1) When the pressure at the mixed gas outlet 8′ changes due to mechanical ventilation, it will be prevented by the pressure compensation unit 2′ consisting of spiral pipeline that the gas may reversely flow due to pressure change to bring the gas carrying the anesthetic vapor to the fresh gas inlet 1′ so as to influence the concentration output; (2) When the pressure at the fresh gas inlet 1′ changes, the pressure compensation unit 2′ consisting of spiral pipeline will attenuate the change of the gas caused by the pressure change and stabilize the flow speed of the gas.
However, this kind of anesthetic vaporizer typically has the following disadvantages: (1) Although there is a temperature compensation unit, since the temperature compensation unit and the pressure compensation unit are independent to each other, then when in use, the temperature compensation unit is unable to change the temperature of the vaporizer and the pressure compensation unit is unable to serve the function of adjusting temperature, the two units cannot be combined together, resulting in that when in use, the temperature of the vaporizer will gradually drops and accordingly the vaporization speed of the anesthetic agent will slow down and the deviation of the concentration of the anesthetic vapor in the outputted mixed gas from the set concentration will be increased, over time; (2) When being placed outside the vaporizer, the pressure compensation unit occupies the space outside the vaporizer so that the structure of the vaporizer is not compact, and when being placed inside the vaporizer, the pressure compensation unit is required to be assembled together with other units so that the structure and assembly are complicated.